Miniaturization trends in Electronics have begged solutions for mounting various large components.
Among these, quartz crystal resonators are among the most difficult due to their physical size in the most common frequency range of 3.0 MHz to 20.0 MHz. In addition, quartz crystal resonators mounted in positions other than the intended position require mechanical dampening for shock and vibration.
The current solution is to mount these devices horizontally. While this mounting scheme requires more P.C. board "Real Estate", the height is reduced by a factor of over 3 to 1. This allows for smaller overall assembly area and more compact designs.
When mounted horizontally, the device must be mechanically stabilized. There are currently two methods of mechanical stabilization: The first method incorporates a "third lead" welded on the top of the device; the second method uses double coated, pressure sensitive, foam tape.
The "third lead" method does not provide a cushion effect between the crystal and the P.C. board.
The double coated, pressure sensitive foam tape method provides the cushion effect, but requires an extra operation in production. Prior to mounting, the protective strip covering the adhesive must be removed to reveal the coated surface opposite the crystal so the assembly will adhere to the P.C. board. In addition, the heat of wave solder, in some instances, changes the chemical make-up of the glue, and the assembly no longer sticks to the P.C. Board, thereby destroying the cushioning effect.